1. Field of the Invention
The present application relates generally to the manufacturing of composite materials and composite parts and, more particularly, to a multi-function detection liner applied to the composite material.
2. Description of Related Art
High performance fiber reinforced composite materials such as those used in space and aerospace applications are manufactured by impregnating dry fibrous material forms, such as unidirectional fibers or woven fabrics, with uncured resins. A resin impregnated fibrous material is also called a prepreg material or a prepreg. A composite part may be laid-up or formed using an automated fiber material placement process, but may also be laid-up by hand. The process includes layering isolated layers of prepreg material to build composite parts of assorted shapes and sizes. This process permits the construction of almost limitless different shaped and sized parts.
Conventional prepreg manufacturing typically involves one of several different resin impregnation processes. A resin can be applied to a conventional paper liner and transferred to the dry fibrous material or applied directly to the dry fibrous material. The resin is impregnated within the dry fibrous material by applying a heating process to melt and infuse the resin. The heating process may include temperatures of around 200 degrees Fahrenheit or more. Prior to shipping, a portion of the conventional liner is removed. In either situation above, the manufacturing of a laid-up composite part generally includes the application of a conventional paper liner to one or more sides of the prepreg material capable of withstanding the resin infusion pressure at elevated temperatures.
The conventional liner has many disadvantages. A paper liner is often used in prepreg manufacturing processes because paper, when properly selected or engineered, can withstand the heat and pressure exerted by resin impregnation and consolidation, and it often costs less than other material alternatives. However, conventional paper liners have disadvantages. When unintentionally left on a prepreg during layup of the part, the paper liner cannot easily be detected by typical production non-destructive inspection methods, such as Eddy-current, ultrasound, and radiograph. Retention of any portion of the liner between layers can have negative implications. If a liner is found within a composite part, the material would typically need to be reworked or scrapped, thereby resulting negatively in any delivery schedules. Additionally, the composite part could be weakened at the location of the residual liner which may lead to failure of the part while in use.
Due to this disadvantage, paper liners on the prepreg, as received from the material supplier, are typically removed and replaced with two metalized plastic liners, one on each side of the prepreg. These metalized plastic liners are generally detectable by Eddy-current methods but can be difficult to be detected by ultrasound methods, and may not be detected by the radiograph method. It is possible that liners, even though detectable by one method, may not be detected for various reasons, for example, liner size, process protocol, and others. Therefore, it is important that a liner, if embedded in a cured part, can be detected by a plurality of different production non-destructive inspection methods. Replacing paper liners with the metalized plastic liners consists of approximately 40 percent of the total time spent in converting prepreg from an as-received good to finished cut plies ready for layup.
Another disadvantage of conventional liners includes a relative susceptibility to tearing due to a lack of strength in the liner and an inability to withstand the heating process to infuse the resin within the dry fibrous material. A stronger and more detectable liner is needed. A liner capable of meeting the functions of the traditional liner while also being detected by typical production non-destructive inspection methods at various stages of a part manufacturing processes is desired.
Although great strides have been made in liners for prepreg materials, considerable shortcomings remain.
While the system and method of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the application to the particular embodiment disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the process of the present application as defined by the appended claims.